This invention relates to a method for detecting the presence of tetraalkyl lead compounds in automotive gasoline. More particularly, this invention relates to a method for detecting high concentrations of tetraalkyl lead compounds in gasoline, which method is readily carried out on board an automotive vehicle to determine the use of leaded gasoline therein.
It is well-known to improve the octane rating of automotive gasoline by the addition of a metal-containing organic compound such as tetraethyl lead, tetramethyl lead and methylcyclopentadienyl manganese tricarbonyl (MMT). In particular, gasoline containing tetraalkyl lead compounds is readily commercially available. For regular or leaded gasoline, the concentration of lead additives is typically about 0.4 g. Pb per liter. Even gasoline that is commercially designated "unleaded" generally contains a small concentration of lead compounds, typically 0.001 g. Pb per liter, and may permissibly contain as much as 0.013 g. Pb per liter. This invention is also applicable to MMT, which has recently been advanced as a substitute for the tetraalkyl lead compounds. However, the limited commercial use of MMT at this time makes it of secondary significance herein.
When leaded gasoline is used to operate an automotive vehicle that is equipped with a catalytic converter in the exhaust system for emission control purposes, lead-containing combustion products deposit onto the catalyst surfaces and impair their ability to oxidize exhaust hydrocarbons. As a result, the concentration of hydrocarbons in the emitted exhaust gas is substantially increased and may exceed automotive emissions standards. Catalyst performance is extremely sensitive to leaded gasoline use and even a short use, such as a single tankful, will essentially poison the catalyst. Furthermore, once poisoned, catalytic activity is not readily restored. Therefore, vehicles equipped with catalytic converters, require the use of unleaded gasoline only. However, leaded gasoline is occasionally introduced into the fuel supply and used to operate the vehicle, thereby poisoning the converter and increasing hydrocarbon emissions.
It would be advantageous to be able to determine whether the catalytic converter had been poisoned because the vehicle had been improperly operated with leaded gasoline. This determination may be made by monitoring the vehicle fuel to detect the presence of impermissibly high tetraalkyl lead concentrations. Because the gasoline composition in a vehicle periodically changes when additional fuel is introduced into the gas tank, detection would preferably be carried out on board the vehicle and provide a record for later examination. However, prior methods for detecting the tetraalkyl lead concentration involve sample pretreatment, carefully controlled conditions, time-consuming procedures and sensitive instruments. These methods are not readily adapted to be carried out on board a vehicle under typical automotive operating conditions.
Therefore, it is an object of this invention to provide a simple and versatile method and device for determining the concentration of tetraalkyl lead additives in an automotive gasoline sample. The method is performed directly on the gasoline sample without pretreatment and without significantly affecting the gasoline composition or its usefulness as automotive fuel. The method is also adaptable for detecting MMT or other organometallic additives in a gasoline sample. It is also an object of this invention to provide a method of detecting the presence of relatively high concentrations of tetraalkyl lead compounds in automotive gasoline, which method readily distinguishes commercial leaded and unleaded gasolines.
It is a further object of this invention to provide a method adapted to be carried out on board an automotive vehicle to monitor the fuel used therein to determine the amount of tetraalkyl lead compounds present in said fuel. The method of this invention is carried out under normal vehicle operating conditions by means of a portable, rugged device incorporated into the vehicle fuel supply. The method and device can detect if a predetermined significant amount of leaded additives has been used to operate the vehicle.
It is a still further object of this invention to provide a method and device for detecting whether too much leaded gasoline has been used in an automotive vehicle equipped with a catalytic converter of the type requiring the use of unleaded fuel. The method is capable of detecting if leaded gasoline is being used even if the usage is occasional and interspersed with larger quantities of unleaded gasoline.
It is also an object of this invention to provide an electrochemical method for detecting tetraalkyl lead compounds in gasoline, that produces a permanent record, in the form of a metallic lead deposit, which record may be examined by visual, electrical or other suitable means, to determine the amount of said compounds in the gasoline and, more particularly, if the total amount has been excessive. When the method is adapted to monitor a vehicle fuel supply over a prolonged period, the record (deposit) indicates any significant use of leaded gasoline to operate the vehicle requiring unleaded gasoline, which use may have occurred at any time prior to examination, whether or not leaded gasoline is present in the fuel supply at the time of examination.
It is also an object of this invention to provide an electrochemical device adapted to be incorporated into a fuel supply system on board an automotive vehicle to continually monitor the gasoline used therein to detect the presence of an impermissible amount of lead-containing additives, which amount corresponds to a significant use of leaded gasoline. The inexpensive device is of simple, but rugged construction and designed to function under normal vehicle operating conditions.